The present invention is related to treatment of glass waste products, and more specifically to a method and systems for extracting heavy metals from glass waste.
Efficient and environmentally safe techniques to recycle and dispose of glass waste still eludes the waste disposal and recycling industries. If glass waste is not safely disposed of, then the lead (or other heavy metals) included within the glass waste will leach into a community""s water supply. The levels of lead within the drinking water will then exceed was is typically considered safe (5 parts per million (ppm)) and people consuming the water will then begin to experience illness and possible death.
Moreover, recycling glass is manually intensive and expensive. This is so because one vendor of glass may use different concentrations of lead in their glass products than another glass vendor. As a result, in order to recycle the glass waste, the waste must be separated into vendor specific categories so that each vendor receives glass waste that can be reused by them. Glass waste with different concentrations of lead will melt, spread, and solidify at different temperatures, and therefore glass vendors can only reuse glass waste that has the proper amount of lead concentrations that is used in their glass manufacturing process. Waste disposal facilities receive glass waste that is not separated by vendor, and the waste disposal facilities have no effective techniques for automatically separating different glass vending wastes from one another.
Because of the expense and time consuming nature associated with recycling glass waste, many waste disposal facilities have resorted to illegal disposal of glass waste. This is where the glass waste is not properly treated according to state and federal Environmental Protection Agencies (EPAs). This is extremely dangerous to the people that live near any such facility.
Glass waste associated with computer monitors, such as Cathode Ray Tube (CRT) monitors, and television sets are particular troublesome for glass recyclers and waste disposal facilities, because these monitors include high levels of lead. In the past, one solution has been to ship these monitors to other countries for disposal, such as China. However, in recent years these third-world or developing countries have started to refuse these monitors because of the health hazards this waste has created for their citizens.
Presently, the most popular and legal technique for disposing of computer monitors is a smelting technique. A smelting process melts the glass of the monitor at an extremely high temperature and then extracts the lead off the top of the liquid produced. However, the EPA has authorized this process only as a stop gap measure since no other viable technique presently exist to safely dispose of monitor glass. The reason why the EPA has only temporarily authorized this processes is because the process produces toxic gas as a byproduct and cross contaminates the glass with other toxins. Some toxins and other heavy metals produced by the smelting process include Selenium arsenic. Therefore, the EPA realizes that it cannot continue to permit the smelting process to continue indefinitely and is actively pursuing and promoting research to replace the process.
CRT disposal or television disposal is a major environmental challenge for the United States, this challenge continues to escalate as more and more organizations and people continue to buy and dispose of CRT monitors and televisions at alarming rates. The EPA has only authorized two methods of disposal for these monitors; the first is to recycle the monitors by separating glass waste into the appropriate manufacturers associated with the waste (glass-to-glass recycling). The second technique is the smelting process, which the EPA has only approved as a stopgap or emergency measure. Currently, CRT waste is the number two contributor to hazardous lead waste in the United States. This problem will only continue to grow over the next several years as liquid crystal and/or plasma screen technology is integrated into the industry and individuals/organizations accelerate their disposal rates of the CRT monitors.
Accordingly, there is a need for improved techniques to extract heavy metals from glass waste products. The techniques should be environmentally safe, efficient, and practical so that the techniques are readily embraced and adopted by waste disposal facilities.
Briefly and in general terms, a method and systems are provided for extracting heavy metals from glass waste products. The glass waste is crushed to a small size and treated with a solution of water and acid. The acid extracts the heavy metals from the surface of the glass waste. The glass particles and solution are then separated.
More specifically, and in one embodiment, a method to extract metal from glass is presented. Glass is crushed into glass particles. The glass particles having a size of less than about 2 millimeters in diameter are filtered out from the glass particles of larger diameter size. The tank is filled with the filtered glass particles and a solution of water (H2O) and Nitric acid (HNO3). Furthermore, the solution and glass particles are circulated within the tank for a first period of time. Next, the solution is removed from the tank.
In still another embodiment, a system for extracting metal from glass is described. The system includes a grinding device, a screen, a conveyor, a circulating pump, and a solution pumping device. The grinding device crushes glass into glass particles. The screen filters glass particles having a size of about 2 millimeters. Moreover, the conveyor transports the filtered glass to a tank having a solution of water (H2O) and Nitric Acid (HNO3). The circulating pump device circulates the filtered glass particles and the solution for a first period of time. Finally, the solution-pumping device pumps the solution out of the tank.
In yet another embodiment, a system for extracting metal from glass is provided. The system includes a conveyor device, a solution pump, and a separating device. The conveyor device transports glass particles having a size of about 2 millimeters to a processing tank. The solution pump fills the processing tank with a solution of water and acid, where the acid removes lead from the surface of the glass particles. Furthermore, the separating device removes the glass particles from the tank and the solution.